Summary The Eurocopter Lama SA315B, C-GXYM, serial number2634, was engaged in heli-logging operations on the slopes of Sawtooth Mountain, near Buhl Creek, BritishColumbia, using a 150-foot longline. While lifting a load of logs, the pilot experienced difficulties and released the load from the lower hook on the longline. A mechanical screeching sound was heard. The helicopter gained some altitude momentarily but quickly descended and struck the steep, 45-degree slope below. The helicopter was destroyed at impact, and the pilot was fatally injured. The fuel tank ruptured, but no fire occurred. Ce rapport est galement disponible en franais. Other Factual Information The helicopter was operating at 5900feet above sea level. The weather at the time of the accident was reported as clear skies with no wind, and the temperature was about 5C. The density altitude was just over 6000feet. A light layer of snow covered the ground. On the day of the accident, the helicopter had been operating for about 3.5hours and was into the third logging cycle.1 In this particular heli-logging operation, a logging cycle consisted of 20to 30turns.2 Aircraft maintenance engineers on site reported that they had refuelled the helicopter twice that morning, and they estimated that the accident occurred about 15minutes before the next refuelling stop. Before going for fuel, the pilot would normally call ahead to the log-landing area to request that they prepare choker cables to be delivered to the hillside by the helicopter; he had not yet radioed his intention to pick up the chokers from the landing area. Fuel samples were gathered from the airframe fuel filter, the refuelling truck, and the portable refuelling equipment at the helicopter staging area. No contamination was found. Section 4 (Performance) of the Transport Canada-approved rotorcraft flight manual (RFM) contains a speed-altitude graph outlining the in-flight parameters where pilots should avoid continuous operation (seeFigure1). The accident helicopter was used for repetitive heavy-lift (RHL) operations at about 165feet above ground level and was being operated at a height and airspeed combination that had not been demonstrated to permit a successful emergency landing in the event of an engine power loss. Figure1. Speed-altitude graph (Eurocopter) The Eurocopter Lama helicopter is a derivative of the Aerospatiale AlouetteII and AlouetteIII helicopters and flew for the first time in March1969. The accident helicopter, C-GXYM, was manufactured in1976 and had accumulated a total of about 9525flight hours. The engine was a Turbomeca ArtousteIIIB1 (serialnumber781) and had accumulated about 6040total hours in service since new and 2817hours since overhaul. The wreckage was confined to a small area and was recovered. The engine attachments were found broken, and the engine was resting on top of the airframe. It was reported that the engine was operating after impact and subsequently shut down. The fuel tank was ruptured at impact, and investigators noted a strong smell of fuel beneath the wreckage at the accident site. The leading edges of the main-rotor blades were not significantly damaged. Two of the three blades had each fractured near the blade root and bent down and aft. A two-inch branch had punctured the third blade near the tip. The longline remained attached to the aircraft cargo hook and extended back up the hillside in line with the released load and the helicopter wreckage. During the examination of the accident helicopter, it was discovered that the input freewheel unit (IFWU) was missing. The IFWU is designed to allow the helicopter to enter autorotation in case of engine power loss or loss of drive to the main transmission. A search party commissioned by the TSB and provided by the operator found the IFWU by using metal detectors during a 100person-hour search. The IFWU was found about 40feet left of and 10feet forward of the main wreckage. Upon inspection of the retrieved IFWU, investigators noted that the identification data plate was missing. It probably detached during the accident sequence. Markings on the painted surface suggest that at some time the data plate had been glued and attached to the ring or driven head section of the IFWU. Eurocopter engineering drawings locate the data plate on the smaller diameter shaft or hub, on the engine side near the IFWU ring seal. Two similar IFWUs were examined for comparison after this accident: the method of application and placement of the identification data were not consistent. Furthermore, major subcomponent parts, such as the hub (driving shaft with ramps), do not have visible identification data, such as a serial number. The hub may be reused at overhaul of the IFWU. Eurocopter does not attribute a service life limit or cycle limitation for the IFWU. Identification for this component takes the form of data plates or stickers that can become detached and lost. To ensure traceability, Canadian Aviation Regulations require permanent marking of identification information on life-limited components.3 If an identification tag for a component becomes detached and lost, the component will remain airworthy as long as it is serviceable, remains installed in the aircraft, and has historical records to support the component's installation. Subcomponent parts of the IFWU may be returned to service during an overhaul, creating an assembly with a mix of new and older parts. This new assembly maintains the same serial number and becomes, in effect, an on-condition or time-continued component.4 Time-continued components may satisfy overhaul criteria but have subcomponent parts that have accrued time in service and cycles in operation that may jeopardize their future life expectancy or maintenance schedule. These components may not be capable of operating to their mandated time between overhaul (TBO) again. An IFWU's TBO is 1800hours; however, an inspection must be performed at 800hours. The accident helicopter was routinely maintained and inspected at the operator's hangar facility in DeWinton, Alberta, from November2to5. At the time of the accident, the helicopter had flown about 16hours since its scheduled inspection was completed. A review of the technical records revealed no reported incidents or deficiencies that could be related to this accident. After an examination of the engine and components, the engine was run up in an approved engine test cell facility. The engine produced full power, and vibration levels were assessed as acceptable. In general, post-accident examination and analyses have shown that turbine engines suffering in-flight failure exhibit severe damage from the impact forces. These examinations and analyses normally reveal damage attributable to high vibration levels resulting from bearing damage. The centrifugal clutch assembly that couples the engine to the main-rotor transmission was disassembled and examined; it was unremarkable. The IFWU and drive shaft assembly was disassembled and examined at the TSB regional wreckage examination facility. It had accumulated 1090hours since overhaul and 1015hours since installation on C-GXYM. There were indications that the IFWU had malfunctioned. The cage that retains and locates the rollers was found broken in several places, and the rollers themselves showed indications of skidding. The cage/retainer, which is not normally subjected to loading forces, exhibited heavy wear. This wear occurs when the IFWU is allowed to freewheel during normal operations; the freewheeling causes the two rotating shafts of the IFWU to alternately disengage and engage under various in-flight load conditions. The two Nadella needles that join the two parts of the bushing set were found fractured; this damage allowed the cage to be slightly misaligned and lowered the spring tension. Damage to the tangs of the outer bushing indicated violent disengagement (spit-out) where the rollers are ejected from the wedge (pinch angle) formed between the ramp of the hub shaft and the ring. Using a scanning electron microscope, chemical analysis, and hardness testing,5 the IFWU was analyzed further and the component material was evaluated for conformity with the manufacturer's specifications. Eurocopter provided expertise during the examination and produced a report.6 The Eurocopter accident investigation group also had investigated previous similar accidents and had produced functional, dimensional, and application investigative reports.7 The IFWU showed signs of distress related to repeated high loading. A large number of loading cycles8 related to the RHL external load operation will accelerate the removal of material (wear) from the load-bearing surfaces by the processes of spalling (surface contact fatigue) and abrasive wear. The materials of the load-bearing surfaces are deformed during loading cycles and fatigue over time. RHL external load operations create varying loads in flight that impose fluctuating pressures on the load-bearing contact surfaces. The helicopter remote hook was equipped with a gas shock to minimize impact forces transferred to the airframe by sudden jerks imposed on the longline. After the examination of the accident IFWU, the operator removed the IFWU (serialnumberC-560) from another Lama helicopter (C-GZXX) operating in similar heli-logging conditions. This IFWU had accumulated about 1114hours since overhaul and 837hours since it was last inspected after a main-rotor blade strike incident. An examination of this IFWU revealed that, although it had not malfunctioned, it exhibited wear that exceeded the overhaul rejection criteria and that was similar to the wear found on the accident IFWU. A third IFWU (serialnumber3-C1622) provided by a different operator was also examined. This IFWU had accumulated 1495hours since overhaul and had not been inspected in accordance with the Eurocopter 800-hour inspection requirement. It had also been subjected to RHL external load operations. The freewheel shaft was measured: the wear on the ramps exceeded the tolerance. Lama helicopter components are not subjected to cycle count, except for the metal main-rotor blades and some component parts of the engine. Eurocopter assumes an average of six load cycles per hour for the metal blades used in sling operations. Helicopters engaged in RHL external load operations may experience as many as 30cycles per hour and sometimes more. Some helicopter manufacturers assume an average number of six cycles per hour when designing aircraft components and determining a maintenance schedule. The airworthiness limitations section in the Eurocopter maintenance manual states, If the average flying time between two landings is less than ten minutes, apply to the manufacturer for special instructions. The TBO for the Lama's IFWU is not based on the number of operating cycles. Eurocopter considers time-in-service the only parameter for TBO. The IFWU and the drive shaft assembly are lubricated by the main transmission oil system through a metered orifice in a goose-neck-type injector that directs oil through the centre of the drive shaft to lubricate the driving gears at both ends of the drive shaft and the IFWU internal subcomponent parts. The IFWU rotates at about 6000rpm during normal engine operation. The lubricating oil is centrifuged, and much of the contaminants introduced or generated within the unit are trapped. This design does not constitute a closed circuit, because the oil drips back to the transmission, and it does not provide for the flushing of generated wear debris. Eurocopter incorporated several modifications to this system and reverted back to the jet-type injection of lubricating oil. The most recent revision incorporated a larger orifice at the oil jet. The Eurocopter Lama RFM lists acceptable oils for the main and tail gearbox lubrication; one of these comes under specification MIL.L.2105. Information provided by the operator indicates that the oil used - a Shell Spirax HD, described as a heavy duty automotive gear oil - conformed with US specification MIL.L.2105D. Eurocopter reported having examined a distressed IFWU from an African operator and determining that the lubricating oil was contaminated and that the internal parts were excessively worn. Eurocopter also examined another IFWU malfunction in a Lama accident in Italy in October1991. As a result of these accidents, Eurocopter issued service bulletin SB05-31 on 19August1993, requiring an inspection of the IFWU every 800hours to check for wear and contamination until the 1800-hour scheduled overhaul. This inspection was later incorporated in the maintenance manual in Section5.20 as a separate component inspection, distinct from the T2 (800-hour) airframe inspections. A caution note accompanied the inspection procedures, alerting operators of the requirement to perform this inspection in accordance with WorkCardNo.40-13-603. To accomplish this inspection, the IFWU is disassembled. Field technicians are required to ascertain the wear on the subcomponent moving parts at that time. Eurocopter does not issue overhaul criteria to field operators, reserving this function for overhaul-trained and certified personnel. The work card instructs field technicians to send the IFWU to an approved overhaul facility if wear is detected. Eurocopter and approved repair and overhaul representatives stated that about 80% of hubs returned for the 800-hour inspection or overhaul are removed from service because they fail to meet tolerances. A review of the technical records for the accident helicopter revealed that this inspection had not been carried out on the IFWU. The accident helicopter was equipped with composite main-rotor blades, partnumberLOML3160-100, manufactured in the US by Rotor Trends LLP (Limited Liabilities Partnership). Heli-logging operations require fast turnarounds: to make the operation economically viable, the helicopter must perform a specified number of turns for each logging cycle. In heli-logging, rapid descent and flare may cause the main rotor to accelerate, and the IFWU may disengage (or freewheel) and then re-engage. Although the composite main-rotor blades are more aerodynamically efficient than the original Eurocopter metal blades, both sets of blades can enter autorotation. The degree to which this occurs is dependent on flight profile, pitch angle, density altitude, and aircraft gross weight. In this flight profile (rapid descent and flare), the main rotor may freewheel, but not necessarily. Even a small application of collective pitch during rapid descents will keep the IFWU engaged. Many heli-logging operators mandate a minimum collective pitch angle or torque setting during rapid descent in their standard operating procedures to prevent freewheeling. The RFM makes no provision or consideration for this specific mode of operation where the pilot may not attempt to enter autorotation but the IFWU nevertheless is forced to disengage due to aerodynamic forces that propel the main rotor faster than it is driven. This disengagement may not be readily detectable or indicated by a needle-split on the engine and the main-rotor tachometer. The helicopter manufacturer, Eurocopter France, has not certificated the use of composite blades on the Lama helicopter. The composite blades, however, were approved for use on the Lama by the US Federal Aviation Administration and Transport Canada in accordance with supplemental type certificate No.SH778GL and supplemental type authority No.SH92-13, respectively. In1986, the French certification authority (the Direction Gnrale de l'Aviation Civile) in a reciprocal agreement with participating States, authorized the installation and the use of these blades in France. The RFM supplement, which provides the pilot with particular information concerning the composite blades, had not been incorporated into the TC-approved RFM. The supplement reminds the operator that the weight and power limitations set forth in the RFM are still applicable and that the operator is responsible to ensure that these limitations are observed. The supplement also requires that a specific placard be installed near the collective pitch indicator dial computer on the instrument panel. This placard is to remind the pilot that composite blades are installed and to add 190pounds to the dial computer to establish correct pitch setting in conjunction with a pop-up chart on top of the centre console. The placard was not installed on the accident helicopter. The Lama helicopter is not equipped with a torque gauge or indicator. The pitch indicator shows the angle of attack of the main-rotor blades (as demanded by the pilot through the collective control lever), not the transmission torque. The pilot can manually set the collective pitch dial computer at any time to take into account the outside air temperature, the weight of the helicopter, and the pitch setting required to hover, as determined during a power check. Furthermore, in consultation with the aircraft's pop-up charts, the collective pitch dial computer determines the appropriate maximum pitch setting so as to limit the power applied to the airframe components. The helicopter was equipped with an Onboard Weighing Systems load cell, load meter, and data recorder to inform the pilot of the weights being lifted and to provide the operator with a record of the loads. The load cell system was reported to function erratically for several days before the accident. No data could be extracted from the unit after the crash. In general terms, when heli-logging in the Lama, the pilot focuses outside the helicopter to position it above the load to be picked up and, to some degree, relies on the load metre to determine an acceptable load that could be lifted by the helicopter. The Lama is capable of exceeding the structural limitations of the power train drive components and the weight limitations of the cargo hook system.